Paper width-responsive switch apparatus for printers

ABSTRACT

A system for adjusting a printer to accommodate different widths of paper includes a fixed sprocket wheel and a slidable sprocket wheel for engaging perforations in the margin of the paper. The slidable sprocket wheel is positively coupled to a slidable trolley which has a pair of opposed but spaced cams projecting therein which operate individually and sequentially on a row of switches by shifting followers projecting from each individual switch. The present system is disclosed as being used with an electrostatic raster printer in which a series of nozzles direct streams of ink onto a sheet of paper to thereby print on the paper. The streams of ink are controlled by the switches to convert to a non-printing, or &#39;&#39;&#39;&#39;gun-down,&#39;&#39;&#39;&#39; mode sequentially as the switches are shifted to the first condition. As the switches are shifted to the second condition, the streams of ink are converted sequentially to a printing mode. In this way, those streams of ink which will impinge upon the paper are retained in a printing mode and those streams of ink which will miss the edge or margin of the paper will be placed in a non-printing or gundown mode.

Unite States Patent [191 Hagstrom et al.

[451 Aug. 6, 1974 PAPER WlDTH-RESPONSIVE SWITCH I APPARATUS FOR PRINTERS [75] Inventors: Arthur A. Hagstrom, Hoffman Estates; Takeshi Yamashita, Chicago, both of I11.

[73] Assignee: Teletype Corporation, Skokie, Ill.

[22] Filed: Feb. 8, 1973 [21] Appl. No.: 330,550

[52] US. Cl 200/153 LA, 200/172 A [51] Int. Cl. H0lh 15/00 [58] Field of Search. 200/153 LA, 46, 16 R, 172 A, 200/16 C, 5 C, 18,5 R, 16 D [56] References Cited UNITED STATES PATENTS 3,023,388 2/1962 Girolamo et al. 200/153 LA X 3,217,112 11/1965 Campbell et a1 ZOO/16C 3,369,100 2/1968 Kussy et al 200/172 A 3,719,786 3/1973 Mallett et al. 200/5 EB FOREIGN PATENTS OR APPLICATIONS 424,924 5/1967 Switzerland 200/153 LA Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith Attorney, Agent, or Firm-J. B. Hoofnagle, .Ir.; J. L. Landis [57 ABSTRACT A system for adjusting a printer to accommodate different widths of paper includes a fixed sprocket wheel and a slidable sprocket wheel for engaging perforations in the margin of the paper. The slidable sprocket wheel is positively coupled to a slidable trolley which has a pair of opposed but spaced cams projecting therein which operate individually and sequentially on a row of switches by shifting followers projecting from each individual switch.

The present system is disclosed as being used with an electrostatic raster printer in which a series of nozzles direct streams of ink onto a sheet of paper to thereby print on the paper. The streams of ink are controlled by the switches to convert to a non-printing, or gun-down, mode sequentially as the switches are shifted to the first condition. As the switches are shifted to the second condition, the streams of ink are converted sequentially to a printing mode. In this way, those streams of ink which will impinge upon the paper are retained in a printing mode and those streams of ink which will miss the edge or margin of the paper will be placed in a non-printing or gun-down mode.

6 Claims, 4 Drawing Figures ll lllllllflll' PATENIEU Am; 51924 SHEET 1 [If 3 PATENTED 6'974 3,828,153

samams PATENTEUAUB 81w Y 3.828.153

sumanrs l i Lu I PAPER WIDTH-RESPONSIVE SWITCH APPARATUS FOR PRINTERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to printers, and more particularly, to systems for automatically adjusting a printer to accommodate paper of various widths.

2. Technical Considerations and Prior Art The situation is often encountered in which it is desired to use paper of different widths in the same printer. In modern, high speed printers there is consequently a need for a convenient way to rapidly adapt the printers to accommodate paper of different widths.

One type of modern high speed printer is the electrostatic raster printer in which a bank of nozzles directs streams of electrostatically charged ink drops onto an electrostatically charged sheet of paper. There is usually one nozzle for each two character spaces. The characters are formed by deflecting the streams of ink drops horizontally with arrays of selectively potentialized electrodes while moving the paper vertically. The combined vertical and horizontal motions produce the desired two dimensional characters. Such a printer is disclosed in U.S. Pat. No. 3,641,588 which issued to J. L. Metz.

The aforementioned patent, however, discloses no system for readily adapting the printer to accommodate paper of different widths. Mechanical margin setters which are used on conventional printers and typewriters would not be satisfactory because they are designed for either movable type or movable carriage arrangements. In the electrostatic printer there is no type, as such, and no shiftable carriage.

If paper of a relatively narrow width is used with the electrostatic printer of Metz, the outboard nozzles must convert to a non-printing or gun down mode. However, when relatively wide paper is used, the outboard noz zles must be converted back to a printing mode. This is accomplished in the present invention by automatically correlating the mode of the nozzle to the position of a slidable paper drive sprocket which engages perforations adjacent to the margin of the paper.

SUMMARY OF THE INVENTION In accordance with the principals of the present invention, a preferred embodiment of a printer may include an adjustable member which may be a sprocket wheel used for engaging marginal perforations in sheets of paper. The adjustable member is slidably mounted on a structure such as a paper drive spindle. The location of the slidable adjustable member in relation to a fixed member such as a fixed sprocket wheel, is indicative of the width of the paper being printed upon. As the adjustable member is slid, it operates a row of switches by engaging the switches individually and sequentially with a device such as a sliding trolley. The switches convert printing assemblies, such as ink stream nozzles, sequentially to a gun-down mode as the adjustable member is moved toward the fixed member. When the adjustable member is moved away from the fixed member, the switches convert the printing assemblies sequentially to a printing mode.

In further accordance with the invention, the individual switches may include spring contacts which are secured to cam followers restrained to move laterally of the path followed by the adjustable member and the sliding trolley. The followers are shifted in one direction upon being engaged by a first cam mounted on the trolley. Upon being engaged by a second cam mounted on the trolley in opposed spaced relation to the first cam, the followers are shifted in the opposite direction.

BRIEF DESCRIPTION OF THE DRAWINGS In the ensuing detailed description, reference is made to the accompanying drawings in which:

FIG. 1 is a schematic view in perspective of a printer in which a series of nozzles dispense streams of ink drops that are electrostatically deflected in a horizontal plane to record horizontal portions of print on a sheet of paper while the sheet of paper is moved vertically to record vertical portions of print;

FIG. 2 is a perspective view of a paper advancing mechanism, according to the principles of the present invention, wherein a movable sprocket is coupled to a row of sliding switches by a trolley in order to correlate the number of nozzles in a printing mode to the width of paper being printed on by the printer of FIG. 1;

FIG. 3 is a cross-section taken along line 33 of FIG. 2 showing how a single sliding switch is coupled to the movable sprocket by the trolley; and

FIG. 4 is a cross-section partially broken away and taken along line 44 of FIG. 3 showing a pair of opposed but spaced cams located in the trolley which engage individually a series of followers to operate the switches.

DETAILED DESCRIPTION OF THE INVENTION GENERAL OPERATION OF THE PRINTER Referring now more particularly in FIG. 1 of the drawings, there is shown generally a printing assembly 10 such as an electrostatic printer, with which the present invention may be advantageously used. The assembly 10 is substantially similar in operation to the raster printer disclosed in the aforementioned U.S. Pat. No. 3,641,588. It includes an ink reservoir 12 which is connected by conduits 14 to a bank of electrically conductive heads 16. Each head 16 has a delivery nozzle 18 in which sufiicient pressure is maintained to produce meniscuses from the downstream end of the nozzles resulting in intrusions of ink drops 20. Spaced downstream of the nozzles 18 is an electrically conductive platen 22 which has a potential opposite that of the ink drops 20 so as to attract them.

A sheet of paper 24 is arranged to be moved in the direction of an arrow 25 over the upstream face of the platen 22 by an axially fixed rotatable sprocket wheel 26 and a selectively axially slidable rotatable sprocket wheel 27 (FIG. 2), each having an associated circumferential array of sprocket pins 26a (or 27a) which engage a different marginal row of apertures 29 (only one marginal row shown) in the paper 24. The sprocket wheels 26 and 27 are mounted on a spindle 28 which is rotated by a pulley 30 that is driven by a motor 31 coupled thereto with a timing belt 32. Further details of one preferred sprocket-spindle arrangement is disclosed in a copending application of B. L. Shevick, Ser. No. 243,749, filed May 13, 1972, and assigned to the assignee of the present invention.

In order to electrostatically control the drops of ink 20, conventional charging methods are utilized in which terminals 34 and 36 are connected to the heads 16 and the platen 22, respectively, to produce an electrostatic charge on the ink as it passes through the heads and to provide a potential difference between the drops and the platen. In order to generate an electro static field of sufficient magnitude to draw ink into streams of drops 26 and to initiate ink movement in a trajectory toward platen 22, valving electrodes 33 are disposed downstream of the nozzles 18. The valving electrodes have apertures 39, coaxially aligned with the bores of nozzles 18, through which the stream of ink drops continuously flow under sufficient impelling force to impinge on the paper 24. Only one valving electrode 38 is shown in the drawing for the sake of clarity; however there is actually one valving electrode for each of the nozzles 43.

A pair of parallel electrodes 43 and 44 (only one pair is shown) are spaced downstream of each valving electrode 33 and are generally vertically spaced about the ink drop trajectory permitting passage therebetween of the stream of drops 20. Charging means, of which only terminals 46 and 47 are shown, are adapted for imposing one of two selected voltage conditions across the electrodes 43 and 44. In the first condition, electrodes 43 and 44 are either in an on or an of printing mode. In the "on printing mode the drops 20 follow the trajectory 43. In the off printing mode the drops 20 are deflected from the trajectory 48 to the trajectory 49. In the second condition, the electrodes 43 and 44 are in a gun down mode deflecting the ink drops 20 to follow a gun-down trajectory 50. A mask 51 is disposed downstream of electrodes 43 and 44 to intercept the drops following the trajectories 49 and 50 while allowing the drops 20 following the trajectory 48 to continue toward and impinge on the paper 24.

A horizontally spaced pair of parallel electrodes 52 and 53 are mutually disposed relative to the trajectories 48, 49, and 50 downstream of electrodes 43 and 44. A sweep generator 54 is connected to the electrodes 52 and 53 through pairs of leads 55 to deflect drops 20 repeatedly in a generally horizontal direction. By known means, the sweep generator 54 is adapted to change left electrodes 52 from a high to a base value while increasing simultaneously the charge on the right electrode 53 from the base value to a high value. After each voltage sweep, the generator restores the electrodes 52 and 53 to an initial neutral condition in preparation for a repeat sweep. Consequently, drops 20 which are passing between the horizontal electrodes 52 and 53 as they follow the path 43 are moved from the left to the right in a manner such that a straight line of ink dots 56 will be traced or printed on the paper 24 transversely of the direction of the arrow for each voltage sweep. Accordingly, one dimension of any visual two dimensional design, such as an alphanumeric character, can be generated on the paper 24 by reason of the horizontal sweep of the stream of ink drops 20.

The vertical dimension of a two dimensional design can be generated by moving the paper 24 in the direction of the arrow 25. This is accomplished by rotating the spindle 23 with the motor 31. When the vertical and horizontal dimensions are combined, they produce two dimensional characters. Character definition is added by applying vertically deflecting voltages to the electrodes 43 and 44 such that selected drops 20 from groups thereof, which would be associated with selected line traces, if printed, follow the trajectory 49 and are intercepted by the mask 51. Control of the vertical electrodes 43 and 44 through terminals 47 and 46 is in accordance with conventional programming. A master controller 57 coordinates the operation of the horizontal electrodes 5H and 52, the vertical electrodes 43 and 44 and the motor 30 in accordance with an input of printing instructions.

A trough S8 is positioned to drain the mask 51 and thereby collect fluid produced along the trajectories 49 and 50. Suitable means, such as a pump 60, which is connected to the trough 53 is adapted to return the ink caught by the mask 51 to the reservoir 12. The foregoing construction precludes the requirement for shutting off ink flow from nozzles llt) during the printing operation thereby minimizing the likelihood of nozzle cloggage which occasionally occurs in systems which do not maintain continuous flow from the nozzles during printing.

ADJUSTABLE PAPER ADVANCE SYSTEM If the printing assembly 110 of FIG. 1 is to be used with paper 24 of various widths, then some facility must be provided to conveniently correlate the number of heads 16 in a printing mode to the width of the paper. In other words, for narrower widths of paper 24, some of the outboard" nozzles 18 have to be switched to the gun-down mode. This causes each related stream of ink drops 26 continuously to follow the trajectories 50, strike the mask SI and drain into the trough 58.

The gun-down mode is achieved by placing a high repulsive charge on the upper electrodes 43 located adjacent to those nozzles 18 which would direct streams of ink away from the paper 24. The repulsive charge, of course, is of the same polarity as the charge on the ink drops 20 so as to cause them to follow the deflective gun-down trajectories 50. By converting the trajectories 48 and 49 of the ink drops 20 to the gundown trajectory 50, the ink can be kept flowing through the nozzles I3 thereby preventing clogging.

Referring now to FIG. 2, there is shown an embodiment of an adjustable paper advance system generally designated by the numeral 64 and which may be used with the type of printing assembly 10 broadly illustrated in FIG. ll. As mentioned before, the paper advance system 64 includes the axially fixed rotatable sprocket wheel 26 and the axially slidable rotatable sprocket wheel 27 which are mounted on the spindle 28. The spindle 23 is journalled at both ends in a frame 71 and is driven by the timing belt 32 according to the output of the motor 31 (FIG. l), which is coordinated with the electrodes 43, 44, 52, and 53 by the controller 57, all of which are illustrated in FIG. 1.

In order to accommodate different widths of paper 24, the slidable sprocket wheel 27 is movable back and forth on the spindle 28. For smaller widths of paper 24 (FIG. ll), the sprocket wheel 27 is spaced relatively close to the fixed sprocket wheel 26. For larger widths of paper 24, the sprocket wheel 27 is spaced further form the fixed sprocket wheel 26. In order to insure that the sprocket wheel 27 rotates with the spindle 28, the sprocket wheel 27 has a plurality of keys 65 projecting inwardly therefrom which engage longitudinal keyway slots 66 in the spindle.

The paper 24 (FIG. 1) is held meshed with the sprocket wheels 26 and 26 by a paper retaining bar 72 which has a pair of rollers 73 journalled thereon that hold the paper against a stationary roller 74. The paper retaining bar 72 is secured at each end to arms 76 and 77 which are, in turn, pivoted on a pivot bar 78 attached to the frame 71. When it is necessary to replace the paper 24, the paper retaining bar 72 is lifted, pivoting the arms 76 and 77 about the pivot bar 78. The paper 24 is then passed between the rollers 73 and the roller 74. Upon releasing the paper retaining bar 72, the rollers 73 are brought into contact with and press the paper 24 against the roller 74. Such pressure contact may be effected by gravitational forces, but preferably is produced by biasing means, such as one or more springs (not shown) which spring-bias the pivoting arms '76, 77 downwardly, as viewed in FIG. 2.

A margin indicator or paper width indicator 79 is positioned behind the pivot bar 78. Recorded on the paper width indicator 79 are various standard paper widths such as 3 /3, 4 /2 9 /2 etc. inches.

One of the problems solved by the instant invention is the correlation of the operation of the printing assembly of FIG. 1 to the various widths recorded on the paper width indicator 79. Accordingly, a pointer 81 is slidably mounted adjacent to the pivot bar 78. By its position, as will presently be seen, the pointer 81 transfers information from the indicator 79 to the printing assembly 10.

More specifically, and with reference to FIGS. 2 and 3, the pointer 81 is rigidly secured between a pair of flanges 82 projecting from a slider, generally designated by the numeral 83. The slider 83 is supported slidably by the pivot bar 78, which passes through circular holes 84 in the flanges 82, and by a slider bar 86 which is secured to the frame 71'. The pivot arm 77 is also positioned between the flanges 82 adjacent to the pointer 81 so as to slide with the slider 83 when the latter is moved. Projecting from the pivot arm 77 is a detent 88 (FIG. 3) which engages one of a series of laterally spaced slots 89 formed in a downwardly extending portion of the width indicator 79. These slots 89 correspond in location to the various paper widths marked on the paper width indicator 79. When the paper retaining bar 72 is raised, the arm 77 pivots about the pivot bar 78 removing the detent 88 from a particular slot 89, thereby enabling an operator to slide the slider 83 to a different slot location.

The slider 83 has a slot portion 91 thereon which is curved to complement the spindle 28, and which tits over the movable sprocket wheel 27. Consequently, as the slider 83 and pointer 81 are adjusted to various widths on the paper width indicator 79, the position of the sprocket wheel 27 is adjusted.

Since there are several nozzles 18 per inch of print, the electrodes 44 are switched to the gun-down mode in banks as the pointer 81 is moved to the left as viewed in FIG. 2 and switched to a printing mode in banks as the pointer is moved to the right. As illustrated in FIG. 3, this is accomplished by a series of switches, generally designated by the nuemrals 93, each of which are associated with a particular set of electrodes 43 and 44. The selective operation of the switches 93 connect circuit paths 94 and 96 to achieve gun-down modes or connect circuit paths 94 and 97 to achieve printing modes.

In the illustrated embodiment of FIG. 3, such connections are selectively made by metallic contact springs 98 located in each switch 93. When the contact springs 98 are slid to the left (the solid line position of FIG. 3), paths 94 and 96 are connected, feeding a first predetermined signal to the master controller 57. This signal instructs the controller 57 to apply a gundown voltage to the electrodes 43 and 44 associated with the operated switches 93. When the contact springs 98 are slid to the right (the dotted line position 98a of FIG. 3), the paths 94 and 97 are connected, feeding a second predetermined signal to the master controller 57. This signal instructs the controller to apply a printing voltage to the electrodes 43 and 44 associated with the operated switches 93.

As illustrated in FIGS. 3 and 4, in order to convert the sliding motion of the pointer 81 and the slider 83 into the lateral motion necessary to shift the springs 98, a pair of cams 101 and 102 are disposed to engage followers 103 which are rigidly secured to the springs. The cams 101 and 102 project downwardly from the inner walls of a trolley, generally designated by the numeral 104 which is coupled to the slider 83 by a coupler 106 (FIG. 3) that engages a flange 107 projecting from the trolley. The trolley 104 is tracked on a pair of rails 108 and 109 by pairs of opposed tabs 111 which engage opposite sides of the rails (see FIG. 3).

When an operator moves the pointer 81, the slider 83 moves the trolley 104 along the rails 108 and 1109. As the trolley moves, the cams 101 and 102 individually engage the followers 103. Upon being engaged,the followers 103 move in directions normal to the direction of motion of the trolley 104 because each follower 103 projects through a laterally directed slot 112 in a bracket 113 secured to the frame 71 (see FIG. 3). As best seen in FIG. 4, the cam 101 pushes each follower 103 that it engages in the direction of arrow 114, moving the spring 98 to a printing mode, while the cam 102 pushes eahc follower that it engages in the direction of arrow 116, moving the spring to gun-down mode.

As seen in FIGS. 2 and 3, the trolley 104 is generally U-shaped with two open ends 118 and 119. Consequently, as the trolley 104 is slid along the rails 108 and 109, it slides over the followers 103. The printing mode cam 101 is positioned slightly behind the gun-down mode cam 102 when viewed from the direction of arrow 121 which represents the direction in which the trolley 104 moves to accommodate paper 24 of increased width. Consequently, as the trolley 104 slides in the direction of arrow 121, the printing cam 101 will act after the gun-down mode cam 102, thereby pushing all of the followers 103 that it engages in the direction of arrow 114 and leaving the followers, and thus the springs 98, in the printing mode as illustrated by the dotted lines in FIG. 3. The followers 103 that the trolley 104 has not engaged will be left in the gumdown mode, having been positioned previously by the cam 102.

When it is desired to decrease the width of the paper 24 being printed on, the pointer 81 is moved to the left (FIG. 2) and the trolley 104 consequently moves in the direction of arrow 122. As the trolley so moves, the gun-down mode cam 102 engages the followers 103 after the cam 101 has engaged the followers, thus moving the followers in the direction of arrow 116. This, of course, moves the spring contacts 98 to the gun-down mode, as illustrated by the solid line position of FIG. 3.

By using the staggered cam arrangement as shown in FIG. 4, wherethe cams 101 and 102 have their respective peaks 126 and 127 in opposed, yet spaced relation, a switching mechanism is achieved in which all the switches 93 inboard of the trolley 104 are in a first mode, i.e., the printing mode, and all the switches outboard of the trolley 1 are in a second mode, i.e., the gun-down mode. Thus, as the pointer m is slid back and forth along the paper size indicator 79, the switches 93 change their mode as they are engaged by the trolley 104 to suit the width of the paper 24.

While a specific preferred embodiment of the present invention has been described in detail, it will be obvious that various modifications may be made and alternatives provided without departing from the spirit and scope of the invention.

What is claimed is:

l. A switching system comprising;

a plurality of individual switches arranged in a row;

means on each switch for moving the switch between first and second conditions; and

means including a pair of cams and being movable along the row of switches, wherein one of the pair of cams being movable adjacent one side of the row of switches and the other of the pair of cams being movable adjacent the opposite side of the row of switches, for actuating sequentially each individual moving means to move the switches from the first condition to the second condition as the actuating means moves in a first direction and to move the switches from the second condition to the first condition when the actuating means moves in a second direction.

2. The switching system of claim 1 further including a movable trolley upon which the pair of cams are afixed in opposed, spaced relation whereby one of the pair of cams engages the moving means as the trolley moves in the first direction and the other of the pair of cams engages the moving means as the trolley moves in the second direction.

3. The switching system of claim 2 further including a pair of spaced rails which straddle the row of switches and upon which the trolley is mounted for reciprocation in the first and second directions.

4. The switching system of claim 3 wherein each switch comprises a resilient member which moves with the moving means to effect movement of the switches into the first and second conditions.

5. A switching system comprising:

three spaced, longitudinally extending contact areas;

a plurality of individual switches arrayed in a row in overlying relationship relative to the rows of contact areas, each switch including a resilient contact member which engages a first of the contact areas and selectively either of the remaining contact areas;

a cam follower secured to each of said switches;

a bracket straddling each resilient contact member wherein each bracket has an elongated slot therein which is oriented, relative to an axis extending through the slot, normal to the row of switches, said slot receiving said cam follower and restraining the cam follower to lateral motion in the slot;

a first cam disposed to reciprocate in a direction normal to said defined axis through each of said slots for engaging one portion of each cam follower to move the cam followers successively in a first direction and thereby engage the contact members in a first position with the first of the contact areas and one of the two remaining selectable contact areas;

a second cam disposed to reciprocate in a direction normal to said defined axis through each of said slots for engaging another portion of each cam follower to move the cam followers successively in a direction opposite the first direction and thereby engage the contact members in a second position with the first of the contact areas and the other of the two remaining selectable contact areas; and

means for carrying said cams in fixed opposed relation wherein one of said cams is off-set from the other in the direction in which the cam reciprocate and wherein the first cam is carried adjacent one side of the row of switches and the second cam is carried adjacent the opposite side of the row of switches to move the resilient contact members selectively into the first and second positions.

6. The switching system of claim 5 wherein the carrying means includes:

a pair of rails extending along opposite sides of the row of switches; and

a reciprocating trolley mounted on the rails.

l= l= 4 a 

1. A switching system comprising; a plurality of individual switches arranged in a row; means on each switch for moving the switch between first and second conditions; and means including a pair of cams and being movable along the row of switches, wherein one of the pair of cams being movable adjacent one side of the row of switches and the other of the pair of cams being movable adjacent the opposite side of the row of switches, for actuating sequentially each individual moving means to move the switches from the first condition to the second condition as the actuating means moves in a first direction and to move the switches from the second condition to the first condition when the actuating means moves in a second direction.
 2. The switching system of claim 1 furthEr including a movable trolley upon which the pair of cams are afixed in opposed, spaced relation whereby one of the pair of cams engages the moving means as the trolley moves in the first direction and the other of the pair of cams engages the moving means as the trolley moves in the second direction.
 3. The switching system of claim 2 further including a pair of spaced rails which straddle the row of switches and upon which the trolley is mounted for reciprocation in the first and second directions.
 4. The switching system of claim 3 wherein each switch comprises a resilient member which moves with the moving means to effect movement of the switches into the first and second conditions.
 5. A switching system comprising: three spaced, longitudinally extending contact areas; a plurality of individual switches arrayed in a row in overlying relationship relative to the rows of contact areas, each switch including a resilient contact member which engages a first of the contact areas and selectively either of the remaining contact areas; a cam follower secured to each of said switches; a bracket straddling each resilient contact member wherein each bracket has an elongated slot therein which is oriented, relative to an axis extending through the slot, normal to the row of switches, said slot receiving said cam follower and restraining the cam follower to lateral motion in the slot; a first cam disposed to reciprocate in a direction normal to said defined axis through each of said slots for engaging one portion of each cam follower to move the cam followers successively in a first direction and thereby engage the contact members in a first position with the first of the contact areas and one of the two remaining selectable contact areas; a second cam disposed to reciprocate in a direction normal to said defined axis through each of said slots for engaging another portion of each cam follower to move the cam followers successively in a direction opposite the first direction and thereby engage the contact members in a second position with the first of the contact areas and the other of the two remaining selectable contact areas; and means for carrying said cams in fixed opposed relation wherein one of said cams is off-set from the other in the direction in which the cam reciprocate and wherein the first cam is carried adjacent one side of the row of switches and the second cam is carried adjacent the opposite side of the row of switches to move the resilient contact members selectively into the first and second positions.
 6. The switching system of claim 5 wherein the carrying means includes: a pair of rails extending along opposite sides of the row of switches; and a reciprocating trolley mounted on the rails. 